So I have a 220 Harbor Freight wirefeed welder. Father-in-law got for me last year. Played with it a few times. I pretty much suck, but I can run a crappy bead. Got the helmet/visor and other safety crap too. Nice gift, actually.

So the welder I have can run shielding gas as well. I now have three tanks, one black and unlabeled except for a (Q), one heavy duty helium tank and the other labeled for Nitrogen. Can't find current certification dates on them. No "owner labels", as I returned those with them already.

So here are my questions:

1. Do suppliers swap tanks for tanks? Can I drop off an empty tank and get a full tank of the same size, and effectively just pay for the gas and a surcharge?

2. My Nitrogen tank is green. Can I just take off the "N" sticker and have them fill it with either a plain CO2 or a C-25 mixture? That is, if the tank is certified. This one is 20" high by about 6" in diameter. I think it is what is referred to as a "40".

3. I have another tank that is black, labeled "Q", which equates to an "80" tank.

4. Final tank is a Helium tank, probably a 125 or a 150 based on size.

Any suggestions on what can be done with these would be appreciated.

I'd like one tank for a shield gas, and possibly a pair for an oxy-acetylene torch to play with. How can I trade these tanks to get what I want?

Thanks!